[K2] test problem with VFO and no 7000 kHz signal heard

[Warren Holybee]

Hi, Warren here.

 

I couple years ago I started building a K2. I got it built but was having
issues with the alignment and test, then moved. I just opened the box and
started working on it again.

 

The entire radio is built, but I am still on the Alignment and test part II.
All the tests went well until the VFO Linearization. At first I got a Cal
PLL Info 232, then found that if I increased the VFO to 7180 (which is
outside the 7000-7100 range in the book) that it completes ok. It first I
thought this was fine, but it may be a clue to the other problem I ran into.

 

At the I.F. Amplifier Alignment, I was not able to hear the signal at 7000
kHz. I hear some static that changes in pitch and volume when I adjust AF
gain, RF gain, or L34.

 

I tried a basic signal tracing proceedure on the website (using an antenna
and starting at the cap at the input of the mixer) and got nothing. Several
days of testing later, I jumpered W2 and W3 together and voila, I hear the
internal signal loud and clear right at 7000 kHz.

 

So I'm thinking that either the filter isn't working, or the IF freq. is
off. I am sort of leaning towards the later, given the previous issue with
the Info 232 error. I don't know if it is an issue with the BFO, VFO, or
something else.

 

I don't have a test oscillator, but I do have a spectrum analyzer (8591E)
with a tracking generator. I was thinking of looking at the signal at W2 and
W3 but I don't know what the 50ohm input of the analyzer would do to the
circuit. If it shifts the filter it would be a useless test.

 

One other thing that I don't think is a big deal. I am working in a cold
space about 50 deg. or so. I found that the VCO voltages don't change (and
are all about 6.5V) until it warms up. Just blowing on that area of the
board with my breath a couple times gets it working. Once it is working the
voltages are solid and don't seem to drift day to day. I'm guessing this is
the Thermistor doing it's job and it just can't deal with the cold temp.

 

My test results are below. Suggestions?

 

Thanks,

Warren

 

 

PLL Reference Oscillator Range Test

High 12097.64    Low 12084.22     Range 13

 

VCO Voltages

80m       2.26        5.99

40m       1.7          3.30

30m       2.71        3.21

20m       2.35        3.90

17m       3.08        3.27

12m       3.86        4.22

10m       3.25        4.07

 

BFO High              4916.15

BFO Low                              4911.37

Range                   4.78

 

 

BFO set up exactly as described on page 89.

 

VFO Linearization

Cal PLL Info 232

Set VFO to 7180 and it brought VCO in range and performed the calibration.

 

 

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[Don Wilhelm-4]

Warren,

It appears that you have several problems.  Tackle the CAL PLL/INFO 232
problem first.

Put the internal counter probe into TP1 - then set the K2 frequency to
7000 kHz and measure the frequency using CAL FCTR.  Do you have a valid
frequency reading?  It should be 11915 kHz.
If not, that is the answer to why you fine an INFO 232 when running CAL
PLL.   Try again at a frequency higher in the band (7200 kHz) and see if
you get a frequency reading.

Also of some concern (but not severe) is the 1.7 volts on the R30
voltages when tuned to 7000 kHz.
Are you installing the rework eliminators?   If yes, then did you add
D19 and D20 and change the value of C71 to 120 pF?  If you have done
that, it is also a reason for the CAL PLL failure - go to the secondary
menu and change the parameter for D19 to "Y" and then re-run CAL PLL.

The IF filter problem --
Yes, it would appear that your filter is not working.  Check the
soldering on the crystals in the filter.  The filter impedance is about
150 ohms, but there is a 5 dB pad following the W5 jumper, so you could
inject a 50 ohm signal there, but you would have to transform the output
(at W3) down to 50 ohms - if you have enough sensitivity on the spectrum
analyzer (probably do), you could remove W3 and use a resistive divider
(120 ohms and 50 ohms in series to properly load the filter and provide
a 50 ohm output for the spectrum analyzer - alternately just use a 100
ohm series resistor in the path to the spectrum analyzer input.

Cold start problem --
This is NOT the thermistor.  A problem of that nature can usually be
traced to a soldering problem.  Study the soldering tutorial on the
Elecraft website to see what a good (and bad) solder connection looks
like and look critically at your soldering.  It has been said that a
good solder connection looks like a mountain, but not a volcano - the
'volcano' refers to a circle around a component lead lead where the lead
did not receive sufficient heat, or in the case of a toroid lead, was
not well stripped and tinned.  If the solder connections look more like
balls of solder, rather than flowing out to an almost invisible edge on
the solder pad, the solder pad did not receive enough heat, and there is
likely too much solder - wick away the excess and re-solder.

73,
Don W3FPR

Warren Holybee wrote:

> Hi, Warren here.
>
>  
>
> I couple years ago I started building a K2. I got it built but was having
> issues with the alignment and test, then moved. I just opened the box and
> started working on it again.
>
>  
>
> The entire radio is built, but I am still on the Alignment and test part II.
> All the tests went well until the VFO Linearization. At first I got a Cal
> PLL Info 232, then found that if I increased the VFO to 7180 (which is
> outside the 7000-7100 range in the book) that it completes ok. It first I
> thought this was fine, but it may be a clue to the other problem I ran into.
>
>  
>
> At the I.F. Amplifier Alignment, I was not able to hear the signal at 7000
> kHz. I hear some static that changes in pitch and volume when I adjust AF
> gain, RF gain, or L34.
>
>  
>
> I tried a basic signal tracing proceedure on the website (using an antenna
> and starting at the cap at the input of the mixer) and got nothing. Several
> days of testing later, I jumpered W2 and W3 together and voila, I hear the
> internal signal loud and clear right at 7000 kHz.
>
>  
>
> So I'm thinking that either the filter isn't working, or the IF freq. is
> off. I am sort of leaning towards the later, given the previous issue with
> the Info 232 error. I don't know if it is an issue with the BFO, VFO, or
> something else.
>
>  
>
> I don't have a test oscillator, but I do have a spectrum analyzer (8591E)
> with a tracking generator. I was thinking of looking at the signal at W2 and
> W3 but I don't know what the 50ohm input of the analyzer would do to the
> circuit. If it shifts the filter it would be a useless test.
>
>  
>
> One other thing that I don't think is a big deal. I am working in a cold
> space about 50 deg. or so. I found that the VCO voltages don't change (and
> are all about 6.5V) until it warms up. Just blowing on that area of the
> board with my breath a couple times gets it working. Once it is working the
> voltages are solid and don't seem to drift day to day. I'm guessing this is
> the Thermistor doing it's job and it just can't deal with the cold temp.
>
>  

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